Lisa here. I have been adding possible name derivations for the Black family. Here is a sampling:

Phineas is an English variant of ‘Phinehas,’ a name from the Bible. ‘Phinehas’ probably means “Nubian,” though some believe it means “serpent’s mouth” in Hebrew (BtN). In Greek mythology, Phineus was “a king of Thrace and a prophet. Because he prophesied too truly, revealing too much of the gods’ truth to humans, Zeus blinded him and set the Harpies to plague him.” Phineus later helped the Argonauts by telling them how to get past one of their hazards. (EM)

Isla: ‘Isla’ means ‘island’ in Spanish; it is also the feminine version of a Scottish name referring to the island Islay, which lies off of the west coast of Scotland (BtN). Does not seem to be a star or constellation.

Cygnus: ‘Cygnus’ = a male swan (Latin). In Greek mythology, ‘Cycnus’ was the Musician-king of the Ligurians who was turned into a swan (EM). It is also another name for the constellation called “The Northern Cross.”

Lycoris: Lycoris is the horticultural name for plants in the lily family. In Ovid and Virgil she was a mistress of Marc Antony (Lewis & Short).